1. Field of the Invention
The invention relates to a power output apparatus used for a hybrid vehicle or the like, and more particularly, to a power output apparatus comprising a motor for outputting power, a generator for generating electric power using at least part of the power output by this motor, and an electric motor operated so that the power output to a drive shaft becomes a desired power using the generated electric power or the electric power accumulated after power generation, a hybrid vehicle equipped with the power output apparatus and a method for controlling the operating point of motor.
2. Description of the Related Art
In recent years, various configurations of so-called hybrid vehicles have been proposed for dramatically improving the fuel consumption and exhaust gas purification performance of motors such as gasoline reciprocating engines for outputting power by fuel combustion and at the same time ensuring driving performance. Hybrid vehicles can be subdivided generally into a series hybrid method in which electric power is generated by driving a generator with a motor and an electric motor is driven with the generated electric power to obtain motive force to power the vehicle, and a parallel hybrid method in which a motor and an electric motor are respectively connected to a drive shaft to obtain vehicle motive force by the motor and electric motor. In both methods, the power output from the motor can be output to the drive shaft with arbitrary rotation speed and torque. Therefore, the motor can be driven selecting an operating point of high driving efficiency. As a result, the hybrid vehicle is superior to the conventional vehicle using only a motor as a driving source in the respects of resource-saving and exhaust purification.
Among these methods, in vehicles of the parallel hybrid method, for example, part of the power output from the engine which is a motor is transmitted to the drive shaft through a power adjusting apparatus. The remaining power is converted into electric power by the power adjusting apparatus. This electric power is accumulated in a battery, or used for driving the electric motor as a power source as an alternative to the engine.
As a power adjusting apparatus, for example, a mechanical distribution type power adjusting apparatus using a generator having a rotation shaft, planetary gear having three shafts connected respectively to the drive shaft, engine output shaft and generator rotation shaft, or an electric distribution type power adjusting apparatus using a twin-rotor electric motor comprising a rotor connected to the engine output shaft and a rotor connected to the drive shaft can be applied.
As is already known, the twin-rotor electric motor can transmit a mechanical power from one rotor to the other rotor and at the same time, extract the remaining power as electric power, by controlling the rotation speed difference between the two rotors, namely the sliding amount. In addition, mechanical power can be transmitted to the other rotor while increasing the mechanical power by supplying electric power. Moreover, as publicly known, the planetary gear is such that the rotation speed and torque of the remaining rotation shaft is determined when the rotation speed and torque of two of the three shafts is determined. Based on these characteristics, for example, the remaining power can be extracted as electric power by a generator connected to the remaining rotation shaft, while outputting part of mechanical power input from the rotation shaft connected to the engine output shaft to the drive shaft. It is also possible to increase the power output from the engine and transmit it to the drive shaft by supplying this generator with electric power.
As mentioned above, for the hybrid vehicle, the engine which is a motor can be operated selecting an operating point of higher driving efficiency. So, in the related art of the invention, the engine operating point has been controlled to follow the maximum torque line of relatively high operating efficiency. Here, the maximum torque line is a curved line obtained by connecting points where the torque for each rotation speed is at its greatest in engine rotation speed-torque characteristics.
However, when the engine operating point is controlled to follow the maximum torque line, the following problems have been encountered.
Namely, for example, during driving, when the driver depresses the accelerator pedal in a demand for rapid acceleration, the required power to be output to the vehicle drive shaft increases, and consequently, the power required of the engine also suddenly increases. At this time, as the engine operating point has attained the maximum torque for the rotation speed at that moment by the aforementioned control, the torque can not be increased with the rotation speed of that time, and the power output from the engine does not become equal to the required power immediately. Further, while the engine operating point moves gradually along the maximum torque line according to the increase of the engine rotation speed, power is required for accelerating the inertia as the engine rotation speed increases so the engine operating point takes a considerable amount of time before arriving at the point where power equal to the required power is actually output from the engine, therefore deteriorating the response.
Therefore, it is an object of the invention to provide a power output apparatus that can solve the aforementioned problems of the related art and output the required power from a motor immediately, even when the power required of the motor increases suddenly.
In order to achieve at least part of the foregoing object, the power output apparatus of the invention comprises:
a motor for outputting power;
a generator for generating electric power using at least part of the power output by the motor;
an electric motor operated such that the power output to a drive shaft becomes a desired power using the generated electric power or the electric power accumulated after the generation of electric power; and
a controller for obtaining the power required of the motor based on a predetermined parameter, and controlling an operating point of the motor based on the required power, wherein the controller sets beforehand a predetermined operation line lower in torque than the maximum torque line obtained by plotting the maximum torque for each rotation speed in the relation between the motor rotation speed and torque as a reference operation line for controlling the motor operating point, and controls so as to move the motor operating point along the reference operation line based on the demanded required power in a steady state; and controls the motor operating point such that the power output from the motor becomes the required power by increasing the motor torque while substantially maintaining the motor rotation speed irrespective of the reference operation line when the obtained required power increases.
Thus, in the power output apparatus of the invention, an operation line lower in torque than the maximum torque line is adopted as a reference operation line for moving the motor operating point along the reference operation line in a steady state and for controlling the motor operating point so that the power output from the motor be the required power by increasing the motor torque while substantially maintaining the motor rotation speed irrespective of the reference operation line when the power required of the motor increases.
Therefore, according to the power output apparatus of the invention, even when the power required of the motor increases suddenly, the motor torque increases without increasing the motor rotation speed and the power output from the motor becomes equal to the required power immediately, thereby reducing the time for the motor operating point to arrive at the point where the required power is actually output from the motor such that there is excellent response.
Also, in the power output apparatus of the invention, it is desirable that the controller controls to return the motor operating point to the reference operation line while substantially maintaining the power output from the motor after having controlled the motor operating point such that the power output from the motor becomes equal to the required power by increasing the motor torque while substantially maintaining the motor rotation speed.
By controlling in this way, it is possible to return to the operating point control along the reference operation line in a steady state, smoothly, while satisfying the required power.
Further, in the power output apparatus of the invention, when the motor comprises an engine, it is preferable that the controller increases the motor torque by adjusting the position of a throttle valve of the engine or the opening/closing timing of an intake valve.
Thus, the motor (engine) torque can be increased rapidly to a desired torque by adjusting the position of the throttle valve or the opening/closing timing of the intake valve.
The hybrid vehicle of the invention is a hybrid vehicle equipped with the aforementioned power output apparatus, wherein the wheels are driven by the power output to the drive shaft.
The hybrid vehicle of the invention is able to respond immediately to the demands of the driver. For example, during driving, even when the driver depresses the accelerator pedal in a demand for rapid acceleration, power equal to the required power can be extracted from the motor immediately.
The motor operating point control method of the invention is a method for controlling the motor operating point in a power output apparatus comprising a motor for outputting power, a generator for generating electric power using at least part of the power output by the motor, and an electric motor operated such that the power output to a drive shaft becomes a desired power using the generated electric power or the electric power accumulated after the generation of electric power, comprising steps of:
setting a predetermined operation line lower in torque than the maximum torque line obtained by plotting the maximum torque for each rotation speed in the relation between the motor rotation speed and torque as a reference operation line for controlling the motor operating point;
obtaining the power required of the motor based on a predetermined parameter;
controlling the motor operating point to move along the reference operation line based on the obtained required power; and
controlling the motor operating point such that the power output from the motor becomes equal to the required power by increasing the motor torque while substantially maintaining the motor rotation speed irrespective of the reference operation line when the required power increases.
Therefore, according to the motor operating point control method of the invention, similar to the case of the aforementioned power output apparatus of the invention, even when the power required of the motor increases suddenly, the motor torque increases without increasing the motor rotation speed and the power output from the motor becomes equal to the required power immediately, thereby reducing the time for the motor operating point to arrive at the point where the required power is actually output from the motor such that there is excellent response.